Earlier the day I tried to install the mailman security update, which triggered a debconf dialogue which warned about an existing installation. To avoid potentially overwriting an unpuppetised local configuration I selected the offered "abort" to investigate further, which quit the preinst. That didn't leave apparent changes to the installation.
Later on there was an Icinga alert for qrunner not running and I restarted mailman. When it disappeared later on again I noticed that the puppet run has triggered a reload of the mailman service, which lead to qrunner not running until I restarted mailman manually:
ESC[mNotice: /Stage[main]/Ssh::Client/File[/etc/ssh/ssh_known_hosts]/content: content changed '{md5}318b42d6506e93f9cb45adbd3d2e0e5b' to '{md5}1c4de80271ec0c284007948a7d37daab'ESC[0m ESC[mNotice: /Stage[main]/Mailman::Listserve/Exec[dpkg-reconfigure mailman]: Triggered 'refresh' from 1 eventsESC[0m ESC[mNotice: /Stage[main]/Mailman::Listserve/File[/etc/mailman/mm_cfg.py]/mode: mode changed '0644' to '0444'ESC[0m ESC[0;32mInfo: /Stage[main]/Mailman::Listserve/File[/etc/mailman/mm_cfg.py]: Scheduling refresh of Service[mailman]ESC[0m ESC[mNotice: /Stage[main]/Mailman::Listserve/Service[mailman]: Triggered 'refresh' from 1 eventsESC[0m ESC[mNotice: Finished catalog run in 191.11 secondsESC[0m ESC[0;32mInfo: Sleeping for 37 seconds (splay is enabled)ESC[0m ESC[0;32mInfo: Retrieving pluginfactsESC[0m ESC[0;32mInfo: Retrieving pluginESC[0m ESC[0;32mInfo: Loading factsESC[0m ESC[0;32mInfo: Caching catalog for fermium.wikimedia.orgESC[0m ESC[0;32mInfo: Applying configuration version '1473251029'ESC[0m ESC[mNotice: /Stage[main]/Mailman::Listserve/Debconf::Set[mailman/site_languages]/Exec[debconf-communicate set mailman/site_languages]/returns: executed successfullyESC[0m ESC[0;32mInfo: Debconf::Set[mailman/site_languages]: Scheduling refresh of Exec[dpkg-reconfigure mailman]ESC[0m ESC[mNotice: /Stage[main]/Ssh::Client/File[/etc/ssh/ssh_known_hosts]/content:
This is likely somehow triggered by the debconf setting mailman/site_languages, so I've stopped puppet on fermium until this is debugged further.